“Pi of the Sky” observation of GRB 080319B

the brightest ever gamma ray burst

During night 2008.03.18/19 the “Pi of the Sky” apparatus located at Las Campanas Observatory was observing the Swift satellite field of view with 10 s exposures from 5:49 UT. At 6:12 UT we observed exceptionally bright optical flash reaching 5.8 magnitudo. It was automatically detected by the flash recognition algorithm.

The first image with the flash visible started 2 s before the Swift trigger GRB 080319B. The flash was registered near the border of the frame. After taking 3 images the alert from the Swift satellite was received and the apparatus moved to position the GRB in the center of the frame. Consequent images show the decay of the source down to 11 magnitudo in 4 minutes. We have published the results as GCN 7439 and 7445.

The “Pi of the Sky” observation combined with the Swift gamma-ray data for the first time confirmed that optical and gamma-ray emission start simultaneously with 10 s precision.

Preliminary light curve:

This observation was the proof of the novel concept of the “Pi of the Sky” project. Usually, optical emission from GRB is observed by telescopes listening to alerts from satellite gamma ray detectors. Signal distribution and turning the telescope take some time and the very first minute of the outburst cannot be observed. The principle of the “Pi of the Sky” project is different. The apparatus monitors continuously large fraction of the sky taking 10 s exposures and detects optical flashes independently, while the satellite information confirms the origin of the flash.

Observing the optical emission during the gamma ray burst which usually last less than 2 minutes is crucial to understand the mechanism releasing enormous amount of energy. It is commonly believed that in the case of GRB longer than 2 s the phenomenon is caused by a collape of a massive star ending with a formation of a black hole. The details of the process however, still remains uncertain.

The most important results of this “Pi of the Sky” observation are:
– measurement of the maximum brightness of GRB 080318B equal to 5.8 magnitudo,
– determination of the length of the rising edge of the light curve to be between 5 and 20 s,
– observing that the begining of the optical emission coincide with the gamma emission within 10 s.

The peak of the GRB 080319B was observed also by TORTORA wide-field optical camera having lower limiting magnitude and superior time resolution. The first exposure with visible source started at T0 + 16 s (S. Karpov et al, GCN 7452). Also RAPTOR observed the field before and during the GRB 080319B. The first image with the visible source started at T0 + 2 s. (P. Wozniak et al. GCN 7464). Swift UVOT telescope started the observation at T0 + 51 s (S. T. Holland et al.)

“Pi of the Sky” cameras in ASAS dome at LCO

“Pi of the Sky” team celebrating the discovery

We would like to thank the staff of the Las Campanas Observatory for their help during installation and maintenance of our telescope We also thank Grzegorz Pojmański for providing the space in the ASAS dome and for a lot of help in making our apparatus operational.